It is known that carbon fibers have particularly beneficial mechanical properties, particularly in terms of strength, Young modulus and density. Because of this they are increasingly used in aeronautics or related fields (fabrication of wind turbine blades of large span and low weight, for example) or for manufacturing sports equipment.
The worldwide carbon fiber production capacity was of 111 785 tons in 2012. It will reach 156 845 t in 2016 and 169 300 t in 2020. Actual production is only a part of these nominal capacities, evaluated at 60% in 2012, 68% in 2016 and 72% in 2020. Demand, meanwhile, was of 47 220 t in 2012. It should reach 74 740 t in 2016 and 102 460 t in 2020. This situation of overcapacity could help maintain competitive prices. The matrices of carbon fiber composites are 72% epoxy (Source: PlusComposites Consortium).
In 2012, 16% of demand comes from aeronautics, 62% from industry, and the rest from other sectors (consumer).
Consequently, carbon fiber recycling is now becoming a major challenge.
A composite material has assets that its components do not have on their own: strength, lightness, thermal insulation, new chemical and mechanical properties, etc.
This performance of course results from the nature of the base materials (reinforcement, matrix and their compatibility). This product is adaptable to innovations and enables the creation of new markets.
Composite materials are thus composed of a reinforcement and a matrix.
The reinforcement gives the composite mechanical strength, and can be carbon fiber, glass fiber, Kevlar, aluminum or titanium.
The matrix generally used in the fabrication of the composite is an epoxy resin, and carbon, polyester, vinyl ester or polyamide are also generally used. The matrix, thermosetting or thermoplastic, allows the transfer of forces to the reinforcement, which is more rigid and stronger.
In aeronautics, high-performance reinforcements are used, with matrices of equally high performance.
However, the main techniques of recycling/re-use of composite materials known to date are not completely satisfactory.
In particular, incineration techniques do not allow for the recovery of materials; they generate toxic gases and allow at best a re-use of energy.
Techniques of pyrolysis (thermal treatment of waste, at controlled temperature and pressure) and solvolysis (water, methanol etc.) in supercritical conditions make it possible to break down resins or to separate them from fibers. They nonetheless remain particularly energy-hungry. In addition, the fibers are broken down on the surface from 500° C., and their mechanical properties are thereby reduced.
The Applicant has already proposed (in her patent FR 2 942 149 in particular) a recycling method that can be used for various types of composite material and for carbon fibers in particular. This method employs several successive treatment stages:                an indirect-effect stage with generation of a mechanical shockwave,        a direct-effect stage with an electric arc, creating an electromagnetic pulse that crosses the bath in which the material to be re-used is located, and lastly        a stage of microwave drying.        